Ovarian hormones can influence motor activity. review main components of the motor system consider role of hormones in altering motor responses by acting on neurons within the basal ganglia and cerebellum

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consider role of hormones in altering motor responses by acting on neurons within the basal ganglia and cerebellum

estrogen plays a major role in facilitating motor responses; an effect seen when comparing females at different stages of their estrus cycle or when comparing males and females

Hormones also can influence sensory perception.

Consider the role of hormones on the process of learning and memory.

review the role of the hippocampus as an important structure involved in learning and memory processes

consider the role of gonadal steroids in altering the morphology of neurons within the hippocampus, and possible differences that exist between males and females in learning and memory; we will also consider the role of adrenal hormones on the process of learning and memory, and the link between elevated levels of glucocorticoids, hippocampal damage and memory loss

extrapyramidal system: composed of all other projection pathways that influence motor control:

basal ganglia

cerebellum

groups of neurons within the brainstem that send projections into the spinal cord

neurons within the basal ganglia and cerebellum are interconnected with the cerebral cortex through a series of feedback loops--one way in which the basal ganglia and cerebellum can influence motor responses

in addition, components of the basal ganglia have been linked to cognitive processes (memory)

two additional brain regions are interconnected with the basal ganglia--subthalamic nucleus and substantia nigra

the basal ganglia forms a variety of interconnected loops with the subthalamic nucleus, substantia nigra, thalamus and cerebral cortex

bottom line: basal ganglia (and associated brain regions) receives input from sensory and motor cortices, it processes and integrates the information, and then sends the output to supplementary and premotor cortices to control motor activity

degeneration of neurons within the striatum including neurons that synthesize the neurotransmitters GABA and acetylcholine

effect of this cell loss is disinhibition of motor activity (increased activity)

individuals with this disorder show several symptoms including:

progressive dementia--cognitive deficits

choreiform movements--rapid, irrregular flow of motion associated with fingers, arms and facial muscles; effects can include: “piano-playing” fexion-extension movements of the fingers, elevation and depression of the shoulders and hips, crossing and uncrossing of the legs, and grimacing movements of the face

Huntington’s disease is a hereditary disease; onset of symptoms occurs during the third or fourth decade of life (30s and 40s)

amphetamine--drug that stimulates release of dopamine from nerve terminals in the striatum; secondarily, then the released dopamine will bind to dopamine receptors

haloperidol--dopamine receptor antagonist that acts by blocking dopamine receptors (blocks the ability of dopamine to bind to its receptor)

The administration of apomorphine or amphetamine increases dopamine activity within the brain (including the striatum); two main motoric effects are produced:

first, there is an increase in locomotion and exploratory behavior

second, there is an increase in the display of stereotyped behaviors--repetitive movements of head, whiskers and forelimbs; these repetitive movements can include: chewing movements, excessive sniffing, up/down movements of the head, and so on

Apomorphine stimulates dopamine receptors; reduced levels of dopamine on the lesioned side leads to an increase in dopamine receptors; more dopamine receptors will be activated on lesioned side (greater activity); animal will turn away from lesion.

estrogen levels are elevated during late proestrus-early estrus (prior to, and during the start of behavioral estrus and ovulation); estrogen levels are lower at other times (e.g., diestrus)

dopamine synthesis and release within the striatum is greatest during estrus

administration of amphetamine can stimulate greater release of dopamine in the striatum of female rats in estrus in comparison to females in diestrus; this can be seen in tissue slices of striatum that are placed into a tissue chamber and perfused with amphetamine; this can also be seen in freely moving rats using microdialysisto sample dopamine release within the striatum after administration of amphetamine

administration of amphetamine produced greater levels of stereotyped behavior (such as sniffing and head and forelimb movements) in female rats in estrus in comparison to those in diestrus

you can train female rats to walk across a narrow beam suspended about 3 feet above the floor; task that reflects sensorimotor coordination

you can analyze how well the female does on this task by examining the accuracy of foot placement on the beam--if the foot was placed on top of the narrow beam--”correct”, if the foot slipped off the top or grabbed onto the side--”footfault”

Does performance on this task change over the estrus cycle?

YES--the number of footfaults decrease during estrus; the female rat performs better on task when estrogen levels are high

you can reproduce this effect by administering estrogen directly into the striatum

there are few neurons in the striatum that accumulate estrogen (few estrogen receptors)

effects of estrogen may be nontraditional, that is, estrogen may act at the membrane of nerve terminals to enhance dopamine release versus control of gene transcription; there is evidence for rapid effects of gonadal steroids on membranes (but we don’t know, in most cases, how these rapid effects occur)

it is possible that estrogen may alter other neurocircuits that project to the striatum and that regulate dopamine release (e.g., frontal cortex)

it is also possible that estrogen may influence the amount of dopamine available for release; there are dopamine neurons within the substantia nigra that possess estrogen receptors

however, these latter observations do not explain how estrogen implants within the striatum can alter dopamine release and behavior

the cerebellum receives sensory and motor input, processes the information, and then sends its output (via Purkinje cells) to deep cerebellar nuclei which integrate the input with other motor control systems

bottom line: cerebellum is involved primarily in controlling the timing and pattern of muscles activated during movement, postural support and maintenance of muscle tone

it has been suggested that the rise in estrogen followed by the rise in progesterone may play a role in sensorimotor gating in the cerebellum--influencing how the cerebellum responds to sensorimotor input and its role in controlling motor output

the increases in estrogen and proesterone occur during late proestrus to early estrus and are associated with changes in proceptive and receptive (lordosis) responses; it is possible that changes occurring in Purkinje cell firing rates are associated with proceptive and receptive behaviors; although, how this occurs is not known

of interest, progesterone can bind to GABA-A receptors to potentiate the effects of GABA at its receptor

GABA is an inhibitory neurotransmitter that acts to increase chloride (Cl-) conductance into the cell, with a net effect of increased inhibition

the binding of progesterone to the GABA-A receptor is thought to mediate the decrease in Purkinje cell firing that occurs when progesterone levels are high

also evidence for sex differences in the performance of spatial tasks; gonadal steroids have been implicated in organizational and activational effects on performance

in the adult, changes in hippocampal structure accompany hormone changes during estrus

“brake” on HPA axis

hippocampus possesses mineralocorticoid and glucocorticoid receptors

mineralocorticoid receptors are linked to circadian changes in HPA axis

glucocorticoid receptors are linked to terminating a stress response

chronic exposure to glucocorticoids can damage the hippocampus leading to higher levels of glucocorticoids, more hippocampal damage, and so on; damage to the hippocampus has been linked to memory deficits

an epileptic seizure means that a large collection of neurons in the brain discharge in abnormal synchrony--seizures can be focal that spread throughout cortex or generalized, and may involve loss of consciousness as well as contraction of groups of skeletal muscle

intractable means that his epileptic seizures were resistant to treatment

to stop his epileptic seizures, heunderwent bilateral hippocampectomy--bilateral removal of his hippocampi

following surgery:

GOOD NEWS: his epilepsy stopped

BAD NEWS: while he could remember events early in his life, he could not remember events just prior to surgery (mild form of “retrograde amnesia”), and he was unable to form new memories (“anterograde amnesia:)

Answer--yes! There is evidence for a complex interaction between early experience (rearing), dendritic morphology and sex of individual (rats).

animals raised in an enriched environment possess neurons that are more complex than animals raised under normal laboratory conditions; an enriched environment involves the presence of other animals and various objects to interact with, while normal laboratory conditions are more plain and animals may be housed alone or in small groups with no objects to play with

if you compare males and females housed in the complex environment to rats housed under normal laboratory conditions, you can see several differences:

in the apical dendritic tree of CA3 neurons, females housed in the enriched environment have more dendrites concentrated proximal (close) to the cell body, while males in the enriched environment had more dendrites concentrated distal (far) from cell body

in the dentate gyrus, females housed in enriched environments had granule cells with an increase in dendritic length while males in a similar environment did not show this change

There are numerous examples of differences between males and females in performance on various tests of learning and memory.

Males are “better” at passive avoidance learning than females (e.g., males learn more quickly to not leave a platform because they will get shocked).

Females are “better” at active avoidance learning than males (e.g., females learn to respond more quickly to a cue such as a light or tone that signals that they should move to another part of a chamber to avoid being shocked).

However, Beatty has argued that such differences may simply reflect sex differences in activity. That is, females are more active than males and as a consequence they may do better on active avoidance tasks because of an increased likelihood of making the association between movement to a given part of a chamber , cue presentation and a decrease in shock. Females may do more poorly on passive avoidance tasks because of they can’t sit still.

It is thought that performance on other more complex tasks, such as radial arm maze or the Morris water maze, may be less influenced by sex differences in activity.

Maze tasks are considered tests of spatial abilities in rodents because animals solve these maze tasks by using cues from the surroundings outside of the maze.

The hippocampus (in rats) is thought to be essential for solving tasks that require the animal to use its spatial abilities.

There is evidence that males tend to perform better on spatial tasks than females.

This sex difference in seen in some species but not all.

This difference is also somewhat limited--greatest sex differences are observed during acquisition of the task, and often fewer differences are seen once the task has been learned.

It has been suggested that males and females used different cues to solve spatial tasks (which may underlie differences in acquisition), and there is evidence to suggest that exposure to gonadal steroids during development and in the adult can alter what cues are used to solve a given task.

Question: Does exposure to androgens or estrogens early in life affect spatial abilities in adulthood?

Methods:

4 groups: male rats castrated on day 1 (MNC), sham-operated control males (MC), female rats exposed to estrogen from days 1-10 (FNE), and sham-operated control females treated with oil (FC)

at 45 days of age, all groups were gonadectomized (MNC group was already castrated); this was done to control for any activational effects of on performance

at 70 days of age, all rats were placed on a food deprivation schedule that kept tham at 85% of their free-feeding body weight; rats were trained to run down arms of the maze for food

tested the performance of the rats on locating food pellets when only some of the arms were baited--12-arm maze, 8 arms were baited with food and 4 arms were not; this relationship remained constant throughout the experiment

Question: Why are males and females different in acquisition of the radial arm maze? Do these differences reflect the cues that males and females use to solve the task?

Methods:

similar groups as before: 4 groups: male rats castrated on day 1 (MNC), sham-operated control males (MC), female rats exposed to estrogen from days 1-10 (FNE), and sham-operated control females treated with oil (FC); all groups were gonadectomized

trained the animals on the radial arm maze until high performance levels were obtained

they changed either landmark cues, geometry or both and tested the performance of the animals on task

landmark cues: cues located within or around a maze (table, chair, transport cart); they manipulated these cues by rearranging items or removing them

geometric cues: shape of room (corners of room); manipulated geometry by enclosing the maze within a black circular arena

males and androgenized females used primarily geometry to solve the task

females and feminized males used both geometry and landmarks in performing task

Conclusions:

males use fewer cues (geometry) to solve the radial maze than females (geometry and landmark cues)

the need to learn fewer cues may explain why males acquire the task more quickly than females

enhanced spatial ability in males is promoted by perinatal exposure to gonadal steroids--1) castration of newborn males decreased rate of acquisition, and 2) administration of estrogen to newborn females within first 10 days of life increased rate of acquisition

sex differences can be seen in tasks involving spatial learning and memory

in males:

increased performance may be associated with the use of fewer cues to learn the task (geometry)

gonadal steroids have an organizing effect on spatial ability

rise in testosterone at puberty may also act to enhance spatial abilities (at least on some tasks)--activating effect

in females:

decreased performance may be associated with learning more and possibly different cues associated with a spatial task

in adults, increased estrogen (and associated changes in spine density in the hippocampus) appears to inhibit performance on tasks requiring use of spatial cues but may enhance responsiveness to other cues